Arsenate perturbation of human keratinocyte differentiation

Treatment of cultured malignant human keratinocytes with sodium arsenate greatly suppressed expression of involucrin, a specific marker of keratinocyte differentiation. This action was primarily attributable to inhibition of involucrin transcription according to message run-on and stability measurements. Involucrin was suppressed in nontumorigenic keratinocytes as well, although the efficacy of suppression was less dramatic in cells derived from clinically normal epidermis. Several transition metal oxyanions (vanadate, molybdate, and tungstate) also substantially suppressed involucrin expression, but okadaic acid was ineffective. Immunoblotting detected marked increases in tyrosine phosphorylation of several proteins as a consequence of arsenate treatment of the cultures, while mobility shift analysis revealed a dramatic loss of DNA binding by the transcription factor AP2. These findings support a proposed role for altered levels of protein tyrosine phosphorylation in keratinocyte differentiation. They also suggest that arsenate perturbs the differentiation program in target cells by altering this phosphorylation level and transcription factor activity.